Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!husc6!bbn!oliveb!amdahl!pacbell!noe!marc
From: marc@noe.UUCP (Marc de Groot)
Newsgroups: comp.lang.forth
Subject: Re: Alan Pratt's C-Forth
Message-ID: <685@noe.UUCP>
Date: 8 Oct 89 01:52:05 GMT
References: <4825@cps3xx.UUCP>
Sender: usenet@noe.UUCP
Reply-To: marc@noe.UUCP (Marc de Groot)
Organization: Noe Systems, San Francisco
Lines: 105

In article <4825@cps3xx.UUCP> jhl@frith.egr.msu.edu () writes:
>I am using Alan Pratt's C-Forth under SCO XENIX 386 2.3.1 and have the
>following problem:
>
>In the editor, when I edit an existing block, mark it for updating,
>and flush it out to disk, exit forth, restart forth and look at the
>block file, the original block is unchanged and the block which results
>from my modifications appears at the end of the block file. 

C-Forth contains significant errors, especially in the disk I/O code.
Try the following fixes.  I have not used the interpreter extensively
but these fixes seem to work on preliminary testing.

The following piece of code contains a fix for the problem you
mentioned.  See the first comment below.  This code fragment
replaces getblockfile() in forth.c

getblockfile()
{
	/* M000 Changed the file mode from "a+" to "r+" on next line
	 * and added the call to fseek. Also added the declaration
	 * of ftell() and fopen().
	 */
	long ftell(); /* M000 */
	FILE *fopen(); /* M000 */

	if ((blockfile = fopen(bfilename, "r+")) == NULL) /* M000 */
		errexit("Can't open blockfile \"%s\"\n", bfilename);
	fseek(blockfile, 0L, 2); /* M000 */
	bfilesize = ftell(blockfile);

	printf("Block file has %d blocks.\n",(int) (bfilesize/1024) - 1);
}

In prims.c replace prslw() with the following code.  SLOWSTACK should not
be defined.  Cell should be typedef'd to int (or whatever is the correct
Forth cell size).  

prslw()
{
	unsigned cell buffer, addr; /* M002 */ /* M003 */
#ifdef SLOWSTACK /* M004 */
	cell pop(); /* M003 */
#endif /* SLOWSTACK -- M004 */
	cell flag; /* M003 */
	int i, temp, unwrittenflag = FALSE; /* M000 */
	long fpos, ftell();
	char buf[1024];		/* holds data for xfer */

	flag = pop();
	buffer = pop();
	addr = pop();
	fpos = (long) (buffer * 1024);

					/* extend if necessary */
	if (fpos >= bfilesize) {
	    if (flag == 0) { 		/* write */
		printf("Extending block file to %ld bytes\n", fpos+1024); /* M001 */
		/* the "2" below is the fseek magic number for "beyond end" */
		fseek(blockfile, (fpos+1024) - bfilesize, 2);
		bfilesize = ftell(blockfile);
	    }
	    else {			/* reading unwritten data */
		unwrittenflag = TRUE;	/* will read all zeroes */
	    }
	}
	else {
		/* note that "0" below is fseek magic number for "relative to
		   beginning-of-file" */
		fseek(blockfile, fpos, 0);	/* seek to destination */
	}

	if (flag) {		/* read */
	    if (unwrittenflag) {	/* not written yet */
		for (i=0; i<1024; i++) mem[addr++] = 0;	/* "read" nulls */
	    }
	    else {			/* does exist */
		if ((temp = fread (buf, sizeof(char), 1024, blockfile)) 
								!= 1024) {
			fprintf (stderr,
				"File read error %d reading buffer %d\n",
					temp, buffer);
			errexit();
		}
		for (i=0; i<1024; i++) mem[addr++] = buf[i];
	    }
	}
	else {	/* write */
		for (i=0; i<1024; i++) buf[i] = mem[addr++];
		if ((temp = fwrite (buf, sizeof(char), 1024, blockfile))
								 != 1024) {
			    fprintf(stderr,
				"File write error %d writing buffer %d\n",
					temp, buffer);
			    errexit();
		}
	}
}


-- 
Marc de Groot (KG6KF)                   These ARE my employer's opinions!
Noe Systems, San Francisco
UUCP: uunet!hoptoad!noe!marc
Internet: marc@kg6kf.AMPR.ORG